Narayan Kamath | fc74cb4 | 2017-09-13 12:53:52 +0100 | [diff] [blame] | 1 | /* Obtained from: https://github.com/iSECPartners/ssl-conservatory */ |
| 2 | |
| 3 | /* |
| 4 | Copyright (C) 2012, iSEC Partners. |
| 5 | |
| 6 | Permission is hereby granted, free of charge, to any person obtaining a copy of |
| 7 | this software and associated documentation files (the "Software"), to deal in |
| 8 | the Software without restriction, including without limitation the rights to |
| 9 | use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies |
| 10 | of the Software, and to permit persons to whom the Software is furnished to do |
| 11 | so, subject to the following conditions: |
| 12 | |
| 13 | The above copyright notice and this permission notice shall be included in all |
| 14 | copies or substantial portions of the Software. |
| 15 | |
| 16 | THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
| 17 | IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
| 18 | FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE |
| 19 | AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
| 20 | LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
| 21 | OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE |
| 22 | SOFTWARE. |
| 23 | */ |
| 24 | |
| 25 | /* |
| 26 | * Helper functions to perform basic hostname validation using OpenSSL. |
| 27 | * |
| 28 | * Please read "everything-you-wanted-to-know-about-openssl.pdf" before |
| 29 | * attempting to use this code. This whitepaper describes how the code works, |
| 30 | * how it should be used, and what its limitations are. |
| 31 | * |
| 32 | * Author: Alban Diquet |
| 33 | * License: See LICENSE |
| 34 | * |
| 35 | */ |
| 36 | |
| 37 | // Get rid of OSX 10.7 and greater deprecation warnings. |
| 38 | #if defined(__APPLE__) && defined(__clang__) |
| 39 | #pragma clang diagnostic ignored "-Wdeprecated-declarations" |
| 40 | #endif |
| 41 | |
| 42 | #include <openssl/x509v3.h> |
| 43 | #include <openssl/ssl.h> |
| 44 | #include <string.h> |
| 45 | |
| 46 | #include "openssl_hostname_validation.h" |
| 47 | #include "hostcheck.h" |
| 48 | |
| 49 | #define HOSTNAME_MAX_SIZE 255 |
| 50 | |
| 51 | #if OPENSSL_VERSION_NUMBER < 0x10100000L |
| 52 | #define ASN1_STRING_get0_data ASN1_STRING_data |
| 53 | #endif |
| 54 | |
| 55 | /** |
| 56 | * Tries to find a match for hostname in the certificate's Common Name field. |
| 57 | * |
| 58 | * Returns MatchFound if a match was found. |
| 59 | * Returns MatchNotFound if no matches were found. |
| 60 | * Returns MalformedCertificate if the Common Name had a NUL character embedded in it. |
| 61 | * Returns Error if the Common Name could not be extracted. |
| 62 | */ |
| 63 | static HostnameValidationResult matches_common_name(const char *hostname, const X509 *server_cert) { |
| 64 | int common_name_loc = -1; |
| 65 | X509_NAME_ENTRY *common_name_entry = NULL; |
| 66 | ASN1_STRING *common_name_asn1 = NULL; |
| 67 | const char *common_name_str = NULL; |
| 68 | |
| 69 | // Find the position of the CN field in the Subject field of the certificate |
| 70 | common_name_loc = X509_NAME_get_index_by_NID(X509_get_subject_name((X509 *) server_cert), NID_commonName, -1); |
| 71 | if (common_name_loc < 0) { |
| 72 | return Error; |
| 73 | } |
| 74 | |
| 75 | // Extract the CN field |
| 76 | common_name_entry = X509_NAME_get_entry(X509_get_subject_name((X509 *) server_cert), common_name_loc); |
| 77 | if (common_name_entry == NULL) { |
| 78 | return Error; |
| 79 | } |
| 80 | |
| 81 | // Convert the CN field to a C string |
| 82 | common_name_asn1 = X509_NAME_ENTRY_get_data(common_name_entry); |
| 83 | if (common_name_asn1 == NULL) { |
| 84 | return Error; |
| 85 | } |
| 86 | common_name_str = (char *) ASN1_STRING_get0_data(common_name_asn1); |
| 87 | |
| 88 | // Make sure there isn't an embedded NUL character in the CN |
| 89 | if ((size_t)ASN1_STRING_length(common_name_asn1) != strlen(common_name_str)) { |
| 90 | return MalformedCertificate; |
| 91 | } |
| 92 | |
| 93 | // Compare expected hostname with the CN |
| 94 | if (Curl_cert_hostcheck(common_name_str, hostname) == CURL_HOST_MATCH) { |
| 95 | return MatchFound; |
| 96 | } |
| 97 | else { |
| 98 | return MatchNotFound; |
| 99 | } |
| 100 | } |
| 101 | |
| 102 | |
| 103 | /** |
| 104 | * Tries to find a match for hostname in the certificate's Subject Alternative Name extension. |
| 105 | * |
| 106 | * Returns MatchFound if a match was found. |
| 107 | * Returns MatchNotFound if no matches were found. |
| 108 | * Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it. |
| 109 | * Returns NoSANPresent if the SAN extension was not present in the certificate. |
| 110 | */ |
| 111 | static HostnameValidationResult matches_subject_alternative_name(const char *hostname, const X509 *server_cert) { |
| 112 | HostnameValidationResult result = MatchNotFound; |
| 113 | int i; |
| 114 | int san_names_nb = -1; |
| 115 | STACK_OF(GENERAL_NAME) *san_names = NULL; |
| 116 | |
| 117 | // Try to extract the names within the SAN extension from the certificate |
| 118 | san_names = X509_get_ext_d2i((X509 *) server_cert, NID_subject_alt_name, NULL, NULL); |
| 119 | if (san_names == NULL) { |
| 120 | return NoSANPresent; |
| 121 | } |
| 122 | san_names_nb = sk_GENERAL_NAME_num(san_names); |
| 123 | |
| 124 | // Check each name within the extension |
| 125 | for (i=0; i<san_names_nb; i++) { |
| 126 | const GENERAL_NAME *current_name = sk_GENERAL_NAME_value(san_names, i); |
| 127 | |
| 128 | if (current_name->type == GEN_DNS) { |
| 129 | // Current name is a DNS name, let's check it |
| 130 | const char *dns_name = (char *) ASN1_STRING_get0_data(current_name->d.dNSName); |
| 131 | |
| 132 | // Make sure there isn't an embedded NUL character in the DNS name |
| 133 | if ((size_t)ASN1_STRING_length(current_name->d.dNSName) != strlen(dns_name)) { |
| 134 | result = MalformedCertificate; |
| 135 | break; |
| 136 | } |
| 137 | else { // Compare expected hostname with the DNS name |
| 138 | if (Curl_cert_hostcheck(dns_name, hostname) |
| 139 | == CURL_HOST_MATCH) { |
| 140 | result = MatchFound; |
| 141 | break; |
| 142 | } |
| 143 | } |
| 144 | } |
| 145 | } |
| 146 | sk_GENERAL_NAME_pop_free(san_names, GENERAL_NAME_free); |
| 147 | |
| 148 | return result; |
| 149 | } |
| 150 | |
| 151 | |
| 152 | /** |
| 153 | * Validates the server's identity by looking for the expected hostname in the |
| 154 | * server's certificate. As described in RFC 6125, it first tries to find a match |
| 155 | * in the Subject Alternative Name extension. If the extension is not present in |
| 156 | * the certificate, it checks the Common Name instead. |
| 157 | * |
| 158 | * Returns MatchFound if a match was found. |
| 159 | * Returns MatchNotFound if no matches were found. |
| 160 | * Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it. |
| 161 | * Returns Error if there was an error. |
| 162 | */ |
| 163 | HostnameValidationResult validate_hostname(const char *hostname, const X509 *server_cert) { |
| 164 | HostnameValidationResult result; |
| 165 | |
| 166 | if((hostname == NULL) || (server_cert == NULL)) |
| 167 | return Error; |
| 168 | |
| 169 | // First try the Subject Alternative Names extension |
| 170 | result = matches_subject_alternative_name(hostname, server_cert); |
| 171 | if (result == NoSANPresent) { |
| 172 | // Extension was not found: try the Common Name |
| 173 | result = matches_common_name(hostname, server_cert); |
| 174 | } |
| 175 | |
| 176 | return result; |
| 177 | } |